Exciting electrode



Oct 10, 1939. TOEPFER' 2,175,858

EXCITING ELECTRODE Filed Nov. 24, 1957 INVENTOR ATTORNEY Patented Oct. 10, 1939 UNITED STATES PATENT OFFICE EXCITING ELECTRODE Pennsylvania Application November 24, 1937, Serial No. 176,299

6 Claims.

My invention relates to pool-type discharge devices, and more particularly to new and useful improvements in the exciting electrodes of such devices.

In the operation of pool-type discharge devices, it has been discovered that some ignitor materials become loose in the holders of such devices. It was also observed that the ignitor material was gradually eaten away along the walls of such ignitors where it maintains contact with the holder. The wearing away of portions of the ignitor may be due to one or more of several causes, namely, the concentration of current at a point where current passes from a material of high conductivity to a material of relatively low conductivity or the formation of cathode spots at points of contact. As the material of the ignitor is eaten away, the line of contact gradually moves towards the upper end of the ignitor until portions of the sides of the ignitor are eaten away, whereupon the ignitor falls out from its holder.

According to my invention, I shall eliminate these destructive features by shaping my ignitors so as to maintain a more uniform distribution of current therein or by providing an insulating means to aid in spreading the flow of exciting current over a greater portion of the ignitor.

It is, therefore, an object of my invention to provide an insulator between a portion of a starting electrode and its holder so that current enters the ignitor essentially at the upper base.

It is a further object of my invention to provide an ignitor so shaped that current concen' tration is virtually eliminated.

Other objects of my invention will be apparent from the following description when read in connection with the accompanying drawing, in which:

Figure 1 represents diagrammatically a discharge device of a type with which my improved ignitor may be used,

Fig. 2 represents in section an ignitor of the usual type and the concentration of currents thereabout,

Fig. 3 represents in section an improved ignitor containing an insulator along the vertical walls of the ignitor; and,

Figs. 4 to 7 illustrate possible modifications of ignitors according to my invention.

The apparatus according to Fig. 1 of my invention comprises a vapor discharge device 3 having an anode 5, a mercury-pool cathode I and a starting electrode 9 of the immersion-ignitor type. The cathode l and anode are externally connected with a load circuit II and some suitable supply circuit l3. To initiate a discharge between the anode 5 and the cathode I, it is essential that the anode 5 is maintained positive with respect to the cathode 1. However, it is also essential to provide an immersion-type starting electrode 9 having its tip I5 projecting into the mercurypool cathode l. The starting electrode 3 is also connected externally to some suitable control device It for supplying exciting current which is adapted to cause conduction of current from the starter 9 into the mercury-pool cathode l at predetermined instances of time with respect to the polarity of the main anode potential [3.

Ordinarily, starting electrodes 9 are composed of some material of high resistivity such as boron carbide and silicon carbide, while the holders IT for securing the starting electrodes 9 in place are of some. metal, or possibly graphite may be used. Due to the relative high difference in the conductivity of the holder H and the starting electrode 9, the path of the exciting current is such that it tends to flow along the lower portion of the holder l1 before entering the starting electrode 9, thus resulting in high current concentration at these points. The heat developed gradually causes a wearing away of portions of the ignitor material so that the line of contact advances towards the upper end of the starting electrode 9. If the upper end of the starting electrode 9 is not adhering to its holder H, the ignitor 9 loosens and falls out into the liquid cathode I.

In Fig. 3, I have illustrated an improved starter 9 in accordance with my invention for reducing or possibly eliminating any current concentration. I provide a suitable insulator I9 such as glass and place it between the metal holder I! and the vertical walls of the ignitor starter 9. This structure permits the current to enter the ignitor 9 only at its upper end with the result that the starting current distributes itself more uniformly along the upper base of the ignitor 9.

It is possible to shape the starting electrode 9 in such fashion that current concentration may be substantially eliminated. For example, Fig. 4 illustrates an ignitor 9 with shoulders 21 extending at the point where it was found that the wearing away process first began. It may be feasible to provide notches at this point sloping at an acute angle with respect to the metal holder I! such as illustrated in Fig. 5. Fig. 6 illustrates alternative modifications of which my invention is capable. For example, the

appropriate shape of the upper base of the starting electrode 9 will be convex. The amount of current entering the ignitor 9 along the points of contact with the holder ll varies inversely with the length of the resistance paths. By keeping the length of these paths more or less uniformly equal, the current likewise will become fairly well distributed until it reaches the neck of the starting electrode 9 where it flows uniformly into the mercury cathode 'I.

In the modification shown in Fig. '7, the metal holder I! has a space projection 23 partly extending through the neck of the starting electrode 9. Thus, the current in passing through the metal holder [7 divides itself into several paths with the resulting reduction in current concentration.

Although I have shown and described certain specific embodiments of my invention, I am fully aware that many modifications thereof are possible. My invention, therefore, is not to be restricted except insofar as is necessitated by the prior art or by the spirit of the appended claims.

I claim as my invention:

1. In a discharge device comprising an anode, a liquid metal cathode, a starting electrode of resistance material supported above and in contact with the surface of said cathode, a holding cap in tight fitting engagement with a portion of said starting electrode, means for sending a current through said starting electrode, a shoulder on said starting electrode so shaped as to reduce current concentration in the neighbor hood of said shoulder.

2. In a discharge device comprising an anode, a liquid metal cathode, a starting electrode of resistance material supported above and in contact with the surface of said cathode, a holding cap in tight fitting engagement with a portion of said starting electrode, a notch on each side of said starting electrode, said notches forming an acute angle with the walls of said cap, a source of exciting current for said starting electrode, the path of said current being such that current concentration is virtually eliminated.

3. A starting electrode for a vapor-electric de vice comprising a body of resistance material including a tapered tip portion and a head portion, a metal cap in good electrical contact with said head portion, said head portion being enlarged with respect to the remainder of the electrode, there being an abrupt shoulder at the point of enlargement.

4. A starting electrode for a vapor-electric device comprising a body of resistance material including a tapered tip portion and a head portion, a metal cap in good electrical contact with said head portion, said head portion being enlarged with respect to the remainder of the electrode, there being an abrupt shoulder at the point of enlargement, and the portion of the head within the metal cap having a convex outer surface.

5. In a vapor-electric device having an anode and a liquid cathode, an immersion type starting electrode comprising a body of resistance material including a tapered tip portion extending into the cathode, a head portion and a substantially straight intermediate portion, a metallic holder for said head portion, said head portion being enlarged with respect to said intermediate portion.

6. In a vapor-electric device having an anode and a liquid cathode, an immersion type starting electrode comprising a body of resistance material including a tapered tip portion extending into the cathode, a head portion and a substantially straight intermediate portion, a metallic holder for said head portion, said head portion being enlarged with respect to said intermediate portion, and a groove in said electrode at the junction of said head and intermediate portion.

ADOLPH H. TOEPFER. 

